Fabric filters usually have a housing in which a plurality of filter bags (up to hundreds or thousands) are arranged. Gas to be cleaned enters the housing and passes through the filter bags, depositing dust on the outside surface of the filter bags; clean gas passes through the filter bags and is thus discharged.
In order to clean the filter bags by removing dust cakes, pressure tanks are provided connected to manifolds having nozzles; valve are provided in order to control the compressed air discharge from the pressure tank.
When the filter bags have to be cleaned, the valve (usually in a closed configuration to prevent compressed air discharge from the pressure tank) is opened and the compressed air passes from the pressure tank through the valve reaching the filter bags, cleaning them and causing the removal of the dust cakes from the filter bags.
The valves have a housing defining a cavity with a plunge slidable within the cavity. A control device is provided, to make the valve to pass from a closed configuration to an open configuration (defined by the position of the plunge) and vice versa. EP 2 816 269 discloses a valve of this type.
Between the plunge and the surface of the housing a gap is defined, to allow compressed gas (e.g. air) to pass from one side of the plunge to the other, allowing valve closing.
The size of the annular gap is desired to be small, because this helps a quick movement of the plunge and thus a quick opening of the valve.
In addition, the size of the gap shall neither be too small, because this would cause defective closing of the valve (e.g. non-closing of the valve), nor too large, because this would prevent opening of the valve because of the leakages.
In practice, the gap size is within a given range. For example the given range can be between 0.15-0.35 millimeters.